eta: ETA bandwidth was off by 1.024

eta: ETA bandwidth was off by 1.024

Same fix as 033bbb51 essentially. Since mtime is a 1000th of a second,
for the usual option of having 1024 be the KB base, we end up being
off by 1.024 if we don't multiply by 1000 before dividing by the
runtime (and then dividing by 1024 to get to next power-of-2).

Signed-off-by: Jens Axboe <axboe@kernel.dk>